The present invention relates to substantially light-insensitive thermographic and photothermogryhic materials having a background for viewing in transmission images produced therewith and recording processes there for.
Thermal imaging or thermography is a recording process wherein images are generated by the use of imagewise modulated thermal energy.
In thermography three approaches are known:
1. Imagewise transfer of an ingredient necessary for the chemical or physical process bringing about changes in colour or optical density to a receptor element containing other of the ingredients necessary for the chemical or physical process followed by uniform heating to bring about the changes in colour or optical density.
2. Thermal dye transfer printing wherein a visible image pattern is formed by transfer of a coloured species from an imagewise heated donor element onto a receptor element.
3. Direct thermal formation of a visible image pattern by imagewise heating of a recording material containing matter that by chemical or physical process changes colour or optical density.
Thermographic materials of type 3 become photothermographic if a photosensitive agent is present which after exposure to UV, visible or IR light is capable of catalyzing or participating in a thermographic process bringing about changes in colour or optical density. Examples of photothermographic materials are the so called xe2x80x9cDry Silversxe2x80x9d photographic materials of the 3M Company, which are reviewed by D. A. Morgan in xe2x80x9cHandbook of Imaging Sciencesxe2x80x9d, edited by A. R. Diamond, page 43, published by Marcel Dekker in 1991.
Particular sorts of thermographic film have a blue background, which can vary in tone and optical density, for example, for applications such as the printing of medical images for viewing in transmission. This blue background is not aesthetic having a number of functional purposes, for example: rendering the brownish tone of developed silver images blue/black, preventing over-exposure of the eyes of the viewer upon viewing in transmission with a view-box and improving image sharpness by reducing light scattering. Current practice is to achieve this blue background by incorporating one or more blue pigments or dyes into the support, thereby avoiding possible interference between the pigment or dye necessary to obtain the blue background and the other functional ingredients in the layer structure which makes up a thermographic material. However, this practice requires pigments and dyes which can withstand the high temperatures involved in kneading these dyes and pigments into the polymer (conventionally polyethylene terephthalate), in extruding the polymer to produce the polymer sheet, in stretching the polymer sheet and in conditioning the resulting support to reduce crimp upon later exposure to high temperatures during coating, drying, conditioning and use. Furthermore, this practice also requires the holding of an inventory of different sorts of blue background support as well as substantially colourless supports for producing a complete range of thermographic materials e.g. from graphics applications requiring a substantially colourless support to medical applications requiring a blue background support. The holding of such an inventory of different sorts of blue background support as well as substantially colourless supports incurs financial penalties due to additional storage and logistical requirements as well as increasing the possibility, easy in the subdued lighting required for the coating of photosensitive thermographic products, of using the xe2x80x9cwrongxe2x80x9d sort of support for the production of a particular thermographic material. This is in addition to possible financial penalties incurred by the possible necessary use of more expensive pigments and dyes in the colouring of the support due to the harsher conditions involved in the incorporation process. There is therefore a necessity for thermographic materials having different blue backgrounds, which can utilize a substantially colourless support.
It is therefore an object of the present invention to provide a substantially light-insensitive thermographic recording material having a blue background which can utilize a substantially colourless support.
It is therefore a further object of the present invention to provide a process for producing a substantially light-insensitive thermographic recording material having a blue background which can utilize a substantially colourless support.
It is therefore another object of the present invention to provide a photothermographic recording material having a blue background which can utilize a substantially colourless support.
It is therefore a still further object of the present invention to provide a process for producing a photothermographic recording material having a blue background which can utilize a substantially colourless support.
Other objects and advantages of the present invention will become clear from the further description and examples.
According to the present invention a substantially light-insensitive thermographic recording material is provided comprising a substantially colourless support and a thermosensitive element containing a substantially light-insensitive organic silver salt, an organic reducing agent for the substantially light-insensitive organic silver salt in thermal working relationship therewith and a binder, characterized in that a blue pigment or dye having an absorption maximum in the wavelength range from 550 to 700 nm is present in the thermosensitive element and/or any other layer on either side of the support which provides a background for viewing in transmission images produced with said thermographic recording material.
According to the present invention a thermographic recording process is also provided comprising the steps of: bringing a substanially light-insensitive thermographic recording material, as referred to above, into the proximity of a heat source; image-wise heating of the thermographic recording material with the heat source; and removing the thermographic recording material from the heat source.
According to the present invention a photothermographic recording material excluding a palladium compound is also provided comprising a substantially colourless support and a photo-addressable thermally developable element containing a substantially light-insensitive organic silver salt, an organic reducing agent for the substantially light-insensitive organic silver salt in thermal working relationship therewith, photosensitive silver halide in catalytic association with the substantially light-insensitive organic silver salt and a binder, characterized in that a blue pigment or dye having an absorption maximum in the wavelength range from 550 to 700 nm is present in the photo-addressable thermally developable element and/or any other layer on either side of the support.
A photothermographic recording process is also provided, according to the present invention, comprising the steps of: bringing a photothermographic recording material, as referred to above, into the proximity of a source of actinic radiation; image-wise exposing the photothermographic recording material with the source of actinic radiation; bringing the image-wise exposed photothermographic recording material into the proximity of a heat source; uniformly heating the image-wise exposed photothermographic recording material; and removing the photothermographic recording material from the heat source.
By substantially light-insensitive is meant not intentionally light sensitive. By a substantially colourless support is meant that no colouring agent has been intentially added.
In a preferred embodiment of the substantially light-insensitive thermographic and photothermographic materials, according to the present invention, the blue pigment or dye has an absorption maximum in the wavelength range from 570 to 630 nm. Suitable blue pigments and dyes for use in the present invention are selected from the group consisting of phthalocyanine dyes, phthalocyanine pigments, indanthrone dyes and indantrone pigments. It is clear that a mixture of blue pigments or dyes can also be used in the present invention.
The blue pigments for use in the present invention are preferably dispersed in the coating medium by the methods described e.g. in EP-A 569 074. Further dispersion techniques which may be used are described in e.g. EP-A 552 646, EP-A 595 821 and U.S. Pat. No. 4,900,652. Preferred mean particle sizes of the dispersed pigments are not more than 2 xcexcm, more preferably not more than 1 xcexcm and most preferably not more than 0.5 xcexcm.
By making use of such blue pigments and dyes substantially light-insensitive thermographic and photothermographic materials with a blue background can be obtained which render the brownish tone of developed silver images blue/black, prevent over-exposure of the eyes of the viewer upon viewing in transmission with a view-box and improve image sharpness by reducing light scattering, while having the additional financial benefits of a reduced inventory of supports, less storage capacity for supports and a reduced probability of coating taking place on the wrong support.
Suitable blue dyes/pigments for use in the present invention are:
BLUE DYE 1=Ceres Blue from Bayer AG (N,Nxe2x80x2-2,6-diethyl-4-methylphenyl)-1,4,-diamino-anthraquinone]
BLUE DYE 2=Orasol Blue from Ciba Geigy AG
BLUE DYE 3=Reflex Blue R54 from Hoechst AG
The thermosensitive element used in the present invention comprises a substantially light-insensitive organic silver salt and an organic reducing agent therefor in thermal working relationship therewith and a binder. The element may comprise a layer system in which the ingredients may be dispersed in different layers, with the proviso that the substantially light-insensitive organic silver salt and the organic reducing agent are in thermal working relationship with one another i.e. during the thermal development process the reducing agent must be present in such a way that it is able to diffuse to the substantially light-insensitive organic silver salt particles so that reduction of the organic silver salt can take place.
Preferred substantially light-insensitive organic silver salts used in the present invention are silver salts of aliphatic carboxylic acids known as fatty acids, wherein the aliphatic carbon chain has preferably at least 12 C-atoms, e.g. silver laurate, silver palmitate, silver stearate, silver hydroxystearate, silver oleate and silver behenate, which silver salts are also called xe2x80x9csilver soapsxe2x80x9d; silver dodecyl sulphonate described in U.S. Pat. No. 4,504,575; and silver di-(2-ethylhexyl)-sulfosuccinate described in EP-A 227 141. Modified aliphatic carboxylic acids with thioether group as described e.g. in GB-P 1,111,492 and other organic silver salts as described in GB-P 1,439,478, e.g. silver benzoate and silver phthalazinone, may be used likewise to produce a thermosensitive silver image. Silver imidazolates and the substantially light-insensitive inorganic or organic silver salt complexes described in U.S. Pat. No. 4,260,677 are also suitable.
The term substantially light-insensitive organic silver salt for the purposes of the present invention also includes mixtures of organic silver salts.
A suspension of particles containing a substantially light-insensitive silver salt of an organic carboxylic acid may be obtained by using a process, comprising simultaneous metered addition of an aqueous solution or suspension of an organic carboxylic acid or its salt; and an aqueous solution of a silver salt to an aqueous liquid, as described in EP-A 754 969.
Suitable organic reducing agents for the reduction of the substantially light-insensitive organic silver salts are organic compounds containing at least one active hydrogen atom linked to O, N or C, such as is the case with, mono-, bis-, tris- or tetrakis-phenols; mono- or bis-naphthols; di- or polyhydroxy-naphthalenes; di- or polyhydroxybenzenes; hydroxymonoethers such as alkoxynaphthols, e.g. 4-methoxy-1-naphthol described in U.S. Pat. No. 3,094,41;pyrazolidin-3-one type reducing agents, e.g. PHENIDONE(trademark); pyrazolin-5-ones; indan-1,3-dione derivatives; hydroxytetrone acids; hydroxytetronimides; 3-pyrazolines; pyrazolones; reducing saccharides; aminophenols e.g. METOL(trademark); p-phenylenediamines, hydroxylamine derivatives such as for example described in U.S. Pat. No. 4,082,901;reductones e.g. ascorbic acids; hydroxamic acids; hydrazine derivatives; amidoximes; n-hydroxyureas; and the like, see also U.S. Pat. Nos. 3,074,809, 3,080,254, 3,094,417 and 3,887,378.
Among useful aromatic di- and tri-hydroxy compounds having at least two hydroxy groups in ortho- or para-position on the same aromatic nucleus, e.g. benzene nucleus, hydroquinone and substituted hydroquinones, catechol and substituted catechols are preferred.
Among substituted catechol, i.e. reducing agents containing at least one benzene nucleus with two hydroxy groups (xe2x80x94OH) in ortho-position, are preferred 1,2-dihydroxybenzoic acid, 3-(3xe2x80x2,4xe2x80x2-dihydroxyphenyl)propionic acid, pyrogallol, polyhydroxy spiro-bis-indane compounds, gallic acid, gallic acid esters e.g. methyl gallate, ethyl gallate and propyl gallate, tannic acid and 3,4-dihydroxy-benzoic acid esters are preferred. Particularly preferred catechol-type reducing agents are described in EP-A 692 733 and EP-A 599 369.
Polyphenols such as the bisphenols used in the 3M Dry Silver(trademark) materials, sulfonamide phenols such as used in the Kodak Dacomatic(trademark) materials, and naphthols are particularly preferred for photothermographic recording materials with photo-addressable thermally developable elements on the basis of photosensitive silver halide/organic silver salt/reducing agent.
During the thermal development process the reducing agent must be present in such a way that it is able to diffuse to the substantially light-insensitive organic silver salt particles so that reduction of the organic silver salt can take place.
The silver image density depends on the coverage of the above defined reducing agent(s) and organic silver salt(s) and has preferably to be such that, on heating above 80 xc2x0 C., an optical density of at least 1.5 can be obtained. Preferably at least 0.10 moles of reducing agent per mole of organic silver salt is used.
The above mentioned reducing agents being considered as primary or main reducing agents may be used in conjunction with so-called auxiliary reducing agents. Auxiliary reducing agents that may be used in conjunction with the above-mentioned primary reducing agents are sulfonamidophenols as described in the periodical Research Disclosure, February 1979, item 17842, in U.S. Pat. Nos. 4,360,581 and 4,782,004, and in EP-A 423 891.
Other auxiliary reducing agents that may be used in conjunction with the above mentioned primary reducing agents are sulfonyl hydrazide reducing agents such as disclosed in U.S. Pat. No. 5,464,738, trityl hydrazides and formyl-phenyl-hydrazides such as disclosed in U.S. Pat. No. 5,496,695 and organic reducing metal salts, e.g. stannous stearate described in U.S. Pat. Nos. 3,460,946 and 3,547,648.
The binder for the thermosensitive element or photo-addressable thermally developable element used in the present invention may be coatable from a solvent or aqueous dispersion and is itself film-forming or must be used together with a film-forming binder.
Film-forming binders coatable from a solvent dispersion and usable in the present invention may be all kinds of natural, modified natural or synthetic resins or mixtures of such resins, wherein the organic silver salt can be dispersed homogeneously: e.g polymers derived from xcex1,xcex2-ethylenically unsaturated compounds such as polyvinyl chloride, after-chlorinated polyvinyl chloride, copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and vinyl acetate, polyvinyl acetate and partially hydrolyzed polyvinyl acetate, polyvinyl acetals that are made from polyvinyl alcohol as starting material in which only a part of the repeating vinyl alcohol units may have reacted with an aldehyde, preferably polyvinyl butyral, copolymers of acrylonitrile and acrylamide, polyacrylic acid esters, polymethacrylic acid esters, polystyrene and polyethylene or mixtures thereof. A particularly suitable polyvinyl butyrals containing a minor amount of vinyl alcohol units are marketed under the trade names BUTVAR(trademark) B76 and BUTVAR(trademark) B79 of Monsanto USA and provide a good adhesion to properly subbed polyester supports
The film-forming binder coatable from an aqueous dispersion used in the present invention may be all kinds of transparent or translucent water-dispersible or water soluble natural, modified natural or synthetic resins or mixtures of such resins, wherein the organic silver salt can be dispersed homogeneously for example proteins, such as gelatin and gelatin derivatives (e.g. phthaloyl gelatin), cellulose derivatives, such as carboxymethylcellulose, polysaccharides, such as dextran, starch ethers etc., galactomannan, polyvinyl alcohol, polyvinylpyrrolidone, acrylamide polymers, homo-or co-polymerized acrylic or methacrylic acid, latexes of water dispersible polymers, with or without hydrophilic groups, or mixtures thereof. Polymers with hydrophilic functionality for forming an aqueous polymer dispersion (latex) are described e.g. in U.S. Pat. No. 5,006,451, but serve therein for forming a barrier layer preventing unwanted diffusion of vanadium pentoxide present as an antistatic agent.
The binder to organic silver salt weight ratio is preferably in the range of 0.2 to 6, and the thickness of the recording layer is preferably in the range of 5 to 50 xcexcm.
The above mentioned binders or mixtures thereof may be used in conjunction with waxes or xe2x80x9cheat solventsxe2x80x9d also called xe2x80x9cthermal solventsxe2x80x9d or xe2x80x9cthermosolventsxe2x80x9d improving the reaction speed of the redox-reaction at elevated temperature. A xe2x80x9cheat solventxe2x80x9d, as used in the present invention, is a non-hydrolyzable organic material which is solid in the recording layer at temperatures below 50xc2x0 C. but becomes a plasticizer for the recording layer in the heated region and/or is a liquid solvent for at least one of the redox-reactants, e.g. the reducing agent for the organic silver salt, at a temperature above 60xc2x0 C.
According to the (photo)thermographic recording material of the present invention the thermosensitive element (or photo-addressable thermally developable element) may also contain at least one polycarboxylic acid and/or anhydride thereof in a molar percentage of at least 20 with respect to all the organic silver salt(s) present and in thermal working relationship therewith. Particularly suitable are saturated aliphatic dicarboxylic acids containing at least 4 carbon atoms, e.g. succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonane-dicarboxylic acid, decane-dicarboxylic acid and undecane-dicarboxylic acid.
Suitable unsaturated dicarboxylic acids are : maleic acid, citraconic acid, itaconic acid and aconitic acid. Suitable polycarboxylic acids are citric acid and derivatives thereof, acetonedicarboxylic acid, iso-citric acid and xcex1-ketoglutaric acid.
Preferred aromatic polycarboxylic acids are ortho-phthalic acid and 3-nitro-phthalic acid, tetrachlorophthalic acid, mellitic acid, pyromellitic acid and trimellitic acid and the anhydrides thereof.
In order to obtain a neutral black image tone in the higher densities and neutral grey in the lower densities the thermosensitive or photo-addressable thermally developable element preferably contains in admixture with the organic silver salts and reducing agents a so-called toning agent known from thermography or photothermography.
Suitable toning agents are succinimide, phthalazine and the phthalimides and phthalazinones within the scope of the general formulae described in U.S. Pat. No. 4,082,901 and the toning agents described in U.S. Pat. No. 3,074,809, 3,446,648 and 3,844,797. Particularly useful toning agents are the heterocyclic toner compounds of the benzoxazine dione or naphthoxazine dione type as described in GB-P 1,439,478, U.S. Pat. No. 3,951,660 and U.S. Pat No. 5,599,647.
In addition to the ingredients the thermosensitive element or photo-addressable thermally developable element may contain additives such as free fatty acids, surface-active agents, e.g. non-ionic antistatic agents including a fluorocarbon group e.g. F3C(CF2)6CONH(CH2CH2O)xe2x80x94H; silicone oil, e.g. BAYSILONE(trademark) xc3x961 A (from BAYER AG, GERMANY); ultraviolet light absorbing compounds; silica; colloidal silica; fine polymeric particles, e.g. of poly(methylmethacrylate); and/or optical brightening agents.
The support for the (photo)thermographic recording material according to the present invention may be transparent or translucent e.g. made of a cellulose ester, e.g. cellulose triacetate; corona and flame treated polypropylene; polystyrene; polymethacrylic acid ester; polycarbonate or polyester, e.g. polyethylene terephthalate or polyethylene naphthalate as disclosed in GB 1,293,676, GB 1,441,304 and GB 1,454,956.
The support may be in sheet, ribbon or web form and subbed or pretreated, if need be to improve the adherence to the thereon coated thermosensitive element or photo-addressable thermally developable element.
Suitable subbing layers for improving the adherence of the thermosensitive element or photo-addressable thermally developable element of the substantially light-insensitive thermographic and photothermographic recording materials of the present invention to polyethylene terephthalate supports are described e.g. in GB-P 1,234,755, U.S. Pat. Nos. 3,397,988; 3,649,336; 4,123,278, U.S. Pat. No. 4,478,907 and in Research Disclosure published in Product Licensing Index, July 1967, p. 6.
Suitable pretreatments of hydrophobic resin supports are, for example, treatment with a corona discharge and/or attack by solvent(s), thereby providing a micro-roughening.
The transparent or translucent support may be colourless or coloured, e.g. having a blue colour.
The outermost layer of the (photo)thermographic recording material on the same side of the support as the thermosensitive element or photo-addressable thermally developable element, used in the present invention, may be a protective layer to avoid local deformation of the thermosensitive element or photo-addressable thermally developable element and to improve resistance against abrasion.
The protective layer preferably comprises a binder, which may be hydrophobic (solvent soluble) of hydrophilic (water soluble). Particularly preferred hydrophobic binders are the polycarbonates described in EP-A 614 769. Hydrophilic binders are, however, preferred for the protective layer, as coating can be performed from an aqueous composition and mixing of the hydrophilic protective layer with the immediate underlayer can be avoided by using a hydrophobic binder in the immediate underlayer.
A protective layer used in the present invention may also contain at least one solid lubricant having a melting point below 150xc2x0 C. and at least one liquid lubricant at least one of these lubricants being a phosphoric acid derivative; and additional dissolved lubricating material and/or particulate material, e.g. talc particles, optionally protruding from the outermost layer. Examples of suitable lubricating materials are surface active agents, liquid lubricants, solid lubricants which do not melt during thermal development of the recording material, solid lubricants which melt (thermomeltable) during thermal development of the recording material or mixtures thereof. The lubricant may be applied with or without a polymeric binder.
Such protective layers may also contain particulate material, e.g. talc particles, optionally protruding from the protective outermost layer as described in WO 94/11198. Other additives can also be incorporated therein e.g. colloidal particles such as colloidal silica.
In addition to the ingredients, the substantially light-insensitive thermographic and photothermographic recording materials of the present invention may contain antihalation or acutance dyes which absorb light which has passed through the photosensitive layer, thereby preventing its reflection. Such dyes may be incorporated into the thermosensitive element, photo-addressable thermally developable element or in any other layer of the substantially light-insensitive thermographic or photothermographic recording material of the present invention. The antihalation dye may also be bleached either thermally during the thermal development process, as disclosed in the U.S. Pat. Nos. 4,033,948, 4,088,497, 4,153,463, 4,196,002, 4,201,590, 4,271,263, 4,283,487, 4,308,379, 4,316,984, 4,336,323, 4,373,020, 4,548,896, 4,594,312, 4,977,070, 5,258,274, 5,314,795 and 5,312,721, or photo-bleached after the thermal development process, as disclosed in the U.S. Pat. Nos. 3,984,248, 3,988,154, 3,988,156, 4,111,699 and 4,359,524. Furthermore the antihalation dye may be contained in a layer which can be removed subsequent to the exposure process, as disclosed in U.S. Pat. No. 4,477,562 and EP-A 491 457. Suitable antihalation dyes for use with infra-red light are described in the EP-A""s 377 961 and 652 473, the EP-B""s 101 646 and 102 781 and the U.S. Pat. Nos. 4,581,325 and 5,380,635.
The photothermographic materials according to the present invention may further include an antistatic layer. Suitable antistatic layers are described in EP-A""s 444 326, 534 006 and 644 456, U.S. Pat. Nos. 5,364,752 and 5,472,832 and DOS 4125758. Particularly preferred antistatic layers are those based on polythiophene as disclosed in EP-A 628 560, U.S. Pat. No. 5,354,613, U.S. Pat. No. 5,372,924, U.S. Pat No. 5,370,981 and U.S. Pat. No. 5,391,472.
The photo-addressable thermally developable element used in the present invention comprises a substantially light-insensitive organic silver salt and an organic reducing agent therefor in thermal working relationship therewith, photosensitive silver halide in catalytic association with the substantially light-insensitive organic silver salt and a binder. The photo-addressable thermally developable element may comprise a layer system in which the ingredients may be dispersed in different layers, with the proviso that the substantially light-insensitive organic silver salt and the organic reducing agent are in thermal working relationship with one another i.e. during the thermal development process the reducing agent must be present in such a way that it is able to diffuse to the substantially light-insensitive organic silver salt particles so that reduction of the organic silver salt can take place; and the photosensitive silver halide is in catalytic association with the substantially light-insensitive organic silver salt.
The photosensitive silver halide used in the present invention may be employed in a range of 0.1 to 90 mol percent; preferably, from 0.2 to 50 mol percent; particularly preferably from 0.5 to 35 mol %; and especially from 1 to 12 mol % of substantially light-insensitive organic silver salt.
The silver halide may be any photosensitive silver halide such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide etc. The silver halide may be in any form which is photosensitive including, but not limited to, cubic, orthorhombic, tabular, tetrahedral, octagonal etc. and may have epitaxial growth of crystals thereon.
The silver halide used in the present invention may be employed without modification. However, it may be chemically sensitized with a chemical sensitizing agent such as a compound containing sulphur, selenium, tellurium etc., or a compound containing gold, platinum, palladium, iron, ruthenium, rhodium or iridium etc., a reducing agent such as a tin halide etc., or a combination thereof. The details of these procedures are described in T. H. James, xe2x80x9cThe Theory of the Photographic Processxe2x80x9d, Fourth Edition, Macmillan Publishing Co. Inc., New York (1977), Chapter 5, pages 149 to 169.
The silver halide may be added to the photo-addressable thermally developable element in any fashion which places it in catalytic proximity to the substantially light-insensitive organic silver salt. Photosensitive silver halide and substantially light-insensitive organic silver salt which are separately formed, i.e. ex-situ or xe2x80x9cpreformedxe2x80x9d, in a binder can be mixed prior to use to prepare a coating solution, but they may be blended for a long period of time prior to use. Furthermore, a process may be used in which a halogen-containing compound is added to the organic silver salt to partially convert the substantially light-insensitive organic silver salt to silver halide, as disclosed in U.S. Pat. No. 3,457,075.
A particularly preferred mode of preparing the emulsion of organic silver salt and photosensitive silver halide for coating of the photo-addressable thermally developable element from solvent media, according to the present invention is that disclosed in U.S. Pat. No. 3,839,049, but other methods such as those described in Research Disclosure, June 1978, item 17029 and U.S. Pat. No. 3,700,458 may also be used.
A suspension of particles containing a substantially light-insensitive silver salt of an organic carboxylic acid is disclosed in EP-A 754 969. A particularly preferred mode of preparing the emulsion of organic silver salt and photosensitive silver halide for coating of the photo-addressable thermally developable element from aqueous media, according to the present invention is that disclosed in unpublished PCT patent application PCT/EP/96/02580, which discloses a photothermographic recording material comprising a photo-addressable thermally developable element comprising a substantially light-insensitive organic silver salt, photosensitive silver halide in catalytic association with the substantially light-insensitive organic silver salt, a reducing agent in thermal working relationship with the substantially light-insensitive organic silver salt and a binder, characterized in that the binder comprises a water-soluble polymer, a water-dispersible polymer or a mixture of a water-soluble polymer and a water-dispersible polymer and particles of the photosensitive silver halide are non-aggregating in the photo-addressable thermally developable element and are uniformly distributed over and between particles of the substantially light-insensitive organic silver salt, at least 80% by number of the particles havig a diameter, determined by transmission electron microscopy, of 540nm.
The photo-addressable thermally developable element of the photothermographic recording material, according to the present invention, may contain a spectral sensitizer, optionally together a with a supersensitizer, for the silver halide. The silver halide may be spectrally sensitized with various known dyes including cyanine, merocyanine, styryl, hemicyanine, oxonol, hemioxonol and xanthene dyes optionally, particularly in the case of sensitization to infra-red radiation, in the presence of a so-called supersensitizer. Useful cyanine dyes include those having a basic nucleus, such as a thiazoline nucleus, an oxazoline nucleus, a pyrroline nucleus, a pyridine nucleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus and an imidazole nucleus. Useful merocyanine dyes which are preferred include those having not only the above described basic nuclei but also acid nuclei, such as a thiohydantoin nucleus, a rhodanine nucleus, an oxazolidinedione nucleus, a thiazolidinedione nucleus, a barbituric acid nucleus, a thiazolinone nucleus, a malononitrile nucleus and a pyrazolone nucleus. Of the above described cyanine and merocyanine dyes, those having imino groups or carboxyl groups are particularly suitable. Suitable sensitizers of silver halide to infra-red radiation include those disclosed in EP-A""s 465 078, 559 101, 616 014 and 635 756, JN""s 03-080251, 03-163440, 05-019432, 05-072662 and 06-003763 and U.S. Pat. Nos. 4,515,888, 4,639,414, 4,713,316, 5,258,282 and 5,441,866. Suitable supersensitizers for use with infra-red spectral sensitizers are disclosed in EP-A""s 559 228 and 587 338 and in U.S. Pat. Nos. 3,877,943 and 4,873,184.
The coating of any layer of the (photo)thermographic recording materials of the present invention may proceed by any thin-film coating technique known in the art. In the coating of web type supports for photographic materials slide hopper coating is preferred, but other coating techniques such as dip coating and air knife coating may also be used. Details about such coating techniques can be found in xe2x80x9cModern Coating and Drying Technologyxe2x80x9d by Edward D. Cohen and Edgar B. Gutoff, published by VCH Publishers, Inc. 220 East 23rd Street, Suite 909 New York, N.Y. 10010.
Thermographic imaging is carried out by the image-wise application of heat either in analogue fashion by direct exposure through an image or by reflection from an image, or in digital fashion pixel by pixel either by using an infra-red heat source, for example with a Nd-YAG laser or other infra-red laser, or by direct thermal imaging with a thermal head.
xe2x80x9cHandbook of Imaging Materialsxe2x80x9d, edited by Arthur S. Diamondxe2x80x94Diamond Research Corporationxe2x80x94Ventura, Calif., printed by Marcel Dekker, Inc. 270 Madison Avenue, New York, N.Y. 10016 (1991), p. 498-502 describes the conversion of thermal printing image signals into electric pulses and their transmission through a driver circuit to a thermal printhead. The thermal printhead consists of microscopic heat resistor elements, which convert the electrical energy into heat via Joule effect. The electric pulses thus converted into thermal signals manifest themselves as heat transferred to the surface of the thermal paper wherein the chemical reaction resulting in colour development takes place. The operating temperature of common thermal printheads is in the range of 300 to 400xc2x0 C. and the heating time per picture element (pixel) may be 50 ms or less, the pressure contact of the thermal printhead with the recording material being e.g. 100-500g/cm2 to ensure a good transfer of heat.
In order to avoid direct contact of the thermal printing heads with a recording material not provided with an outermost protective layer, the imagewise heating of the recording material with the thermal printing heads may proceed through a contacting but removable resin sheet or web wherefrom during the heating no transfer of recording material can take place.
In a particular embodiment of the method according to the present invention the direct thermal image-wise heating of the recording material proceeds is carried out with a thermal head. Suitable thermal printing heads are e.g. a Fujitsu Thermal Head (FTP-040 MCS001), a TDK Thermal Head F415 HH7-1089 and a Rohm Thermal Head KE 2008-F3. Activation of the heating elements can be power-modulated or pulse-length modulated at constant power.
EP-A 622 217 discloses a method for producing a continuous tone image by heating the thermal recording element by means of a thermal head having a plurality of heating elements.
Photothermographic recording materials, according to the present invention, may be exposed with radiation of wavelength between an X-ray wavelength and a 5 microns wavelength with the image either being obtained by pixel-wise exposure with a finely focussed light source, such as a CRT light source; a UV, visible or IR wavelength laser, such as a He/Ne-laser or an IR-laser diode, e.g. emitting at 780 nm, 830 nm or 850 nm; or a light emitting diode, for example one emitting at 659 nm; or by direct exposure to the object itself or an image therefrom with appropriate illumination e.g. with UV, visible or IR light.
For the thermal development of image-wise exposed photothermographic recording materials, according to the present invention, any sort of heat source can be used that enables the recording materials to be uniformly heated to the development temperature in a time acceptable for the application concerned e.g. contact heating with for example a heated roller or a thermal head, radiative heating, microwave heating etc.
The substantially light-insensitive thermographic and photothermographic recording materials of the present invention can be used for the production of transparencies, which are widely used in graphics applications, e.g. in masks or for display purposes, and in the medical diagnostic field in which black-imaged transparencies are widely used in inspection techniques operating with a light box.
Application of the present invention is envisaged in the fields of both graphics images requiring high contrast images with a very steep print density applied dot energy dependence and continuous tone images requiring a weaker print density applied dot energy dependence, such as required in the medical diagnostic field.
The following ingredients were used in the invention and comparative examples of the present invention:
backside layer:
CAB: cellulose acetate butyrate, CAB-171-15S from EASTMAN; AH01 (antihalation dye): 
photo-addressable thermally developable element:
i) silver behenate/silver halide emulsion layer:
GEL: phthaloylgelatin, type 16875 from ROUSSELOT;
SENSI: 
Butvar(trademark) B76: polyvinylbutyral from MONSANTO;
LOWINOX(trademark) 22IB46: 2-propyl-bis(2-hydroxy-3,5-dimethylphenyl)methane from CHEM. WERKE LOWI;
TMABP: tetramethylammonium bromide perbromide;
TMPS: tribromomethyl benzenesulfinate;
MBI: 2-mercaptobenzimidazole;
ii) protective layer:
CAB: cellulose acetate butyrate, CAB-171-15S from EASTMAN;
PMMA: polymethylmethacrylate, Acryloid(trademark) l120N from ROHM and HAAS.
LOWINOX(trademark) 22IB46: 2-propyl-bis(2-hydroxy-3,5-dimethylphenyl)methane from CHEM. WERKE LOWI;